In recent years, machines and apparatuses are obliged to operate under higher temperature or under higher speed and heavier load. For instance, temperature of wheel bearing of automobiles often reaches 150.degree.-200.degree. C. due to friction heat with a disk-brake. Under the circumstances, grease has been desired which is resistant to higher temperature and has long life. As lithium soap-based grease is high temperature resistant, grease containing lithium soap of hydroxyfatty acid and monolithium borate has been proposed (Japanese published examined patent application Nos. 2205/1979 and 47235/1982 and U.S. Pat. No. 4,376,060).
U.S. Pat. Nos. 4,435,299, 3,988,248 and Japanese Kokai No. 212297/1982 disclose greases of lithium soap of hydroxyfatty acid mixed with one element selected from lithium dicarboxylate, lithium tetraborate and lithium phosphate.
U.S. Pat. Nos. 3,912,639, 3,565,802 and 4,401,580 disclose greases containing lithium borate with or without lithium phosphate or lithium phosphite, but not lithium soap of hydroxyfatty acid. U.S. Pat. No. 3,836,467 discloses grease containing lithium phosphate or lithium phosphite, but neither lithium soap of hydroxyfatty acid nor lithium borate.
All of greases referred to above contain only one or two components selected from
Some of the greases have dropping point of as high as 260.degree. C. but are inferior in consistency (penetration) or a parameter of mechanical properties. None of them has dropping point of 260.degree. C. or higher as well as desirable consistency.
It has been found that addition of lithium phosphate to grease containing 12-hydroxystearic acid and lithium borate brings change in dropping point, that the change rate in dropping point varies depending on lithium borate employed, i.e., monolithium borate, dilithium borate or trilithium borate and that increase in dropping point is very large when dilithium borate is employed.